1. Field of the Invention
The present invention relates to an imaging apparatus, and, more particularly, to an arrangement of components having reference features which combine to accurately reference the position of a printhead housing to a machine frame of the imaging apparatus.
2. Description of the Related Art
In a typical in-line color electrophotographic imaging process, latent images are formed on a plurality of photosensitive drums, which are in turn each developed using a predetermined color of toner. Typically, these colors are black, magenta, cyan and yellow. The developed images are then transferred to either an intermediate transfer medium or directly to a sheet of media (such as paper) that travels past the photosensitive drums. The image in each color is created one line at a time, and the lines are oriented at right angles to the direction of travel of the media. The individually-generated images combine to form a full-color image. Thus, in a typical multi-color laser printer, the sheet of media receives color images generated at each of the four image developing stations.
It is recognized that in order for the multi-color laser printer to print accurately, the laser beams for all four colors must be in alignment, both in the scan direction (i.e., the direction the laser sweeps across the photoreceptive medium) and the process direction (feed direction of the print medium). However, providing proper alignment of even a single laser printhead in relation to the sheet of media in the process direction can be difficult. This problem is compounded with the addition of each printhead, since the plurality of printheads must be in registration so that the individual images generated by each printhead can be superimposed correctly when combined.
What is needed in the art is a referencing mechanism that accurately references the position of a printhead housing containing a printhead to a machine frame of the imaging apparatus.
The present invention provides a referencing mechanism that accurately references the position of a printhead housing containing a printhead to a machine frame of the imaging apparatus.
The invention comprises, in one form thereof, an imaging apparatus that includes a machine frame, a printhead housing and a position sensing device. The printhead housing includes a laser printhead which generates a laser beam. The position sensing device includes a position sensing device frame and a position sensor for sensing a position of the laser beam. The position sensing device frame is interposed between the machine frame and the printhead housing. Each of the machine frame, the printhead housing and the position sensing device frame includes at least one reference feature that in combination accurately reference the position of the printhead housing to the machine frame.
An advantage of the present invention is that the position sensing device forms an absolute datum for the printhead housed in the printhead housing, and the position sensing device is directly referenced to the machine frame.
Another advantage of the invention, when applied to a laser printer, is that since the position sensing device forms an absolute datum for the laser printhead housed in the printhead housing, and since the position sensing device is directly referenced to the machine frame, then the position of the sensed laser beam is directly related to a position on the photoconductive drum attached to the machine frame.